Therm-a-Rest MondoKing 3D Review: A Bed-Like Sleep for When You Don’t Need to Compromise

I’ve slept for many nights at a time on a mattress only a couple of inches thick. Sometimes all summer long. Sometimes, I arrive after the sun has gone down, and I throw down camp on whatever approximates flat. 

If I have spare natural light, I might manage the landscape a bit (pack wedged here; rope coiled there), but more often, I’ve accepted the fact of off-kilter sleep. The line I’ve drawn, as I’ve drawn over now into the third decade, has been camping out of my rig. Here, I will accept no compromise, and lately, I’ve been leaning on the Therm-a-Rest MondoKing 3D Sleeping Pad for the role.

I don’t break it out all the time, but when I do, I like to think it means just a bit more. I’ve been using the pad for close to 3 years now, and here’s what I’ve come to love about it, what could be tweaked, and whether I think it’s worth splurging on. (It is.)

In short: The Therm-a-Rest MondoKing 3D is the pad you owe yourself. It is a supremely cushioned and wide sleeping space, and topped with a skin-friendly stretch-knit fabric. It’s also a bit pricey, and the stuff sack/pump sack combo isn’t the best, but these are greatly overshadowed by the quality of sleep you’ll get lying on it.

Looking for a new camping mattress? Check out how the MondoKing 3D compares to the rest of the options out there in GearJunkie’s Best Camping Mattress Buyer’s Guide.

Therm-a-Rest MondoKing 3D: Review

The immediate difference between those skimpy sleeping pads I’ve spent so many nights on and the MondoKing is the box they arrive in. Those that I carry on backpacking trips typically can slip into the mailbox, while the box the MondoKing came in was, in fact, mondo.

That makes sense: The packed size of the MondoKing is a 26″ x 10” roll, making it better ferried by your vehicle. Luckily, packed size isn’t anywhere near my list of concerns when it comes to a camping mattress, and I’ve chucked the MondoKing into the back of my truck enough times now to make it my default choice.

Setup and the Joy of Good Valves

Therm-a-Rest just makes dang good valves. The valves on the MondoKing aren’t even the nicest valves Therm-a-Rest makes (the “fast and light” inflatables come with the brand’s WingLock), but they are still great, and there are two of them on the MondoKing for inflation and deflation.

Both of these valves are one-way, so when you’re either inflating or deflating, you aren’t fighting against yourself. As a self-inflating mattress, the MondoKing packs aboard a core of StrataCore foam that rebounds once you release the pad from its bag. This isn’t quick, nor is it ever really satisfactory for a full night’s sleep, so a few puffs into the inflate valve get it nice and firm.

If you don’t have the luxury of waiting for your luxury pad to inflate all by itself, you can do what I do pretty much every night I use it, and inflate it yourself. The stuff sack doubles as your pump sack on the MondoKing, and mates up to the inflation valve with a solid snap to keep it in place. I’ve found that five solid bags full of air will get it where you’ll want it for sleep.

This do-it-all stuff sack is handy, but it’s not quite the best pump sack I’ve used on a camping mattress. The shape of the pump sack does allow for some Venturi effect to aid in inflation, but it’s also not the easiest or most effective at moving air. The NEMO Vortex Pump Sack is a better version, even though it is separate from the stuff sack for NEMO pads.

Instead of trying to save weight with a two-in-one stuff/pump sack combo, I’d rather Therm-a-Rest tack on a separate bag for in-field inflation. For the price of the mattress, it just makes sense.

If you were deciding between this pad and something comparable, like the EXPED MegaMat, I’d argue that the valves alone on the Therm-a-Rest were a worthy enough tip toward its side of the scale. There’s actually an even bigger reason I’d recommend the MondoKing over the MegaMat, as I’ll get into later.

Vertical Sidewalls, Huge Sleeping Area

There are two size options offered in this pad: the Large (at 25” wide and 77” long), which I’ve been using, and an XXLarge, which adds 3” more in length and 5” more in width. Even in the smaller of the two, the space is luxuriously large for sleeping on, and easy to stretch out into whatever shapes sleep might take you through.

It’s the sidewalls that really make the difference, however. Unlike many backpacking pads, which pinch down at the rails to complete a seam, the walls of the MondoKing are an additional panel of material, making them fully vertical when inflated. This gives you the entire functional width of the pad (where backpacking pads might yield a few inches to the slope).

Due to the huge rectangular sleeping area, my favorite sleeping bag style to use with this pad is a cozy, flannel-lined rectangular bag, such as the Kelty Wayback 20 or REI Siesta Hooded sack. There’s nothing sadder than pairing a plush camp bag with a trim mummy-shaped sleeping pad.

That size also seals the deal for me when compared to other sleeping pads. Compared with the “smaller” of the offered EXPED MegaMat sizes, which is 6 feet long, the MondoKing is almost half a foot longer, making it comfortable for even your tallest friends. And, in the larger of the two offered sizes, the Therm-a-Rest is still 2.5 inches longer when compared. 

Even with the MondoKing choices being $10-20 more expensive, this is the main reason I’d opt for the Therm-a-Rest over the EXPED option.

The Goldilocks Thickness of 4 Inches

After testing many camp mattresses now, I’ve found that 4 inches of camp mattress thickness is the perfect “princess and the pea” amount — and it’s all got to do with underinflation. At 4.25 inches, most folks will be able to run the MondoKing mattress a bit par-inflated, meaning the cushion will be plush.

Anything under 3 inches is a backpacking pad (like the ones I’ve tallied up nights on), and 3-3.5 inches is where your backpacking pads masquerading as camping mattresses begin to show up (the NEMO Quasar 3D is notable). At 4.25 inches, the MondoKing 3D is the ideal thickness for when you don’t have to compromise on comfort at the expense of weight.

There are even thicker camp mattresses out there (the 6-inch–thick EXPED MegaMat Max comes to mind), but unless you’re a strict side-sleeper, I’d argue that it’s just an embarrassment of riches for most campers. 

Room for Improvement

As mentioned previously, the MondoKing isn’t perfect. While functional, the pump/stuff sack combo isn’t the best available, and Therm-a-Rest really ought to just include the pump sack that comes with the new NeoLoft Sleeping Pad, which we’ve also reviewed.

The $250-285 price will also be a bit steep for some backpackers-turned-campers who might otherwise opt to continue using their minimal pads on frontcountry trips. For those, the NeoLoft mentioned above may actually make a better option: It’s a bit cheaper, and treads the line between the back and frontcountry excellently at only 1 pound, 9 ounces.

Finally, a small desire I’ll share (simply because I’ve been spoiled by the functionality of other mattresses): The MondoKing 3D lacks the ability to join two of the pads together to create a larger bed for couples. Therm-a-Rest does offer a Universal Couple Kit, but it’s rudimentary. The EXPED LuxeMat shows how to do it right, and runs low-profile zippers along the side to really mate pads together.

Therm-a-Rest MondoKing 3D Sleeping Pad: Conclusion

The Therm-a-Rest MondoKing 3D is the camp mattress your backpacking pad dreams of becoming one day. It’s close to the perfect dimensions, a solid mix of foam and air support, and operated with some excellent Therm-a-Rest valves.

The price tag does put this pad near the top of the heap when compared to the rest of the market, but 3 years of sleeping on the thing has convinced me that it’s worth it. You could get a similar sleeping surface in the more hybrid Therm-a-Rest NeoLoft — a 4.6-inch–thick option that forgoes the foam insulation and is much more backpackable for it — but at the expense of ultimate comfort.

In the end, that’s truly what the MondoKing is about: ultimate comfort. If you’ve put in your time sleeping at odd angles with the occasional pinecone occupying your lumbar, it may be time to treat yourself to a slice of the frontcountry good life.